1. Field of the Invention
The present invention relates to a nonresonant knock sensor that is mounted on, for example, an internal combustion engine with bolts and that is adapted to convert, when a knocking vibration is generated in the internal combustion engine, the knocking vibration into an electric signal through the use of a piezoelectric element supported by being sandwiched therein and to lead out the voltage signal as an output signal.
2. Background Art
A related knock sensor includes a metallic sleeve which has a cylindrical portion, and a flange portion formed at a lower part of the cylindrical portion, and which is configured so that a screw is formed on an upper outer circumferential surface of the cylindrical portion. Also, a first annular electrode plate is fitted onto the cylindrical portion to be placed on the flange portion through an insulating plate. An annular piezoelectric element is fitted onto the cylindrical portion to be placed on the first annular electrode plate. A second annular electrode plate is fitted onto the cylindrical portion to be placed on the annular piezoelectric electrode plate. Also, an over lapping part is placed onto the cylindrical portion to be placed on the second annular electrode plate. Then, a nut is screwed onto a screw to be mounted thereon. The nut is attached thereto by being tighten so that each of the members is pinch-held between the nut and the flange portion. Also, a synthetic resin case is mold-formed around the metallic sleeve. Each of the members is embedded in the synthetic resin case (see, for example, JP-A-2002-257624).
This annular piezoelectric element is configured so that electrode layers are formed on the entire front and rear surfaces thereof, respectively. The annular piezoelectric element is polarized in the direction of thickness thereof. Also, the first and second annular electrode plates are shaped to have the same inside and outside diameters as those of the annular piezoelectric element. The first and second annular electrode plates are in close contact with the front and rear electrode layers, respectively, to thereby ensure an electrical connection state therebetween. Also, connecting rod portions are outwardly extended from the circumferential edges of the first and second annular electrode plates, respectively. The connecting rod portions are electrically connected to a pair of terminals of a connector portion formed integrally with the synthetic resin case, respectively.
The related knock sensor configured in this manner is attached to an internal combustion engine with bolts inserted in the cylindrical portion of a metal bush. Further, when a knocking occurs in the internal combustion engine, components, such as the annular piezoelectric elements and the overlapping parts, are vibrated with the knocking vibration. This vibration is converted into a voltage signal by the piezoelectric element. This voltage signal is outputted to the outside through a female coupler fitted onto the connector portion, and is supplied to an engine control unit (ECU) adapted to control the internal combustion engine.